Plane of incidence

In optical reflection, the plane of incidence is the plane spanned by the surface normal and the propagation vector of the incoming radiation. In wave optics, the latter is the k-vector of the incoming wave.

Optical polarization directions in presence of reflection take following names: p-polarized waves are linearly polarized waves parallel to the plane of incidence, and "s-polarized" waves are linearly polarized waves perpendicular to the plane of incidence. The names come from German "parallel" and "senkrecht".